Electrodeposition of bright nickel



United States Patent ELECTRODEPOSITION OF BRIGHT NICKEL Frank Passal, Detroit, Mich, assignor to Metal & Thermit Corporation, Woodbridge Township, NJ., at corporation of New Jersey No Drawing. Filed Apr. 21, 1959, Ser. No. 807,771

Claims. (Cl. 204-49) This invention relates to electroplating nickel and more particularly to the electrodeposition of bright nickel.

Nickel electrodeposits as plated from Watts, high chloride, fluoborate, etc., type baths are not bright when plated in thicknesses substantially greater than those of very thin strike or flash coatings. Such deposits do not increase in luster with increasing thickness but rather decrease in brightness until dull matte deposits are obtained. -To obtain bright deposits from such baths in substantial thickness, it is necessary to add certain additives, commonly of organic nature, which in cooperation produce highly lustrous deposits with good rate of brightening. It is a common characteristic of such so-called bright nicke plating baths that the deposits tend to increase in luster with increasing thickness. The practical advantage of these bright-nickel baths is that bright deposits can be obtained on basis metals which have not been polished or which do not have a high starting luster, within reasonable specification thicknesses of nickel. Other concomitant advantages such as, leveling or the ability of the deposits to fill in pores, scratches or other superficial defects of the basis metal, may also be obtained.

Addition agents useful as brighteners in nickel plating baths are generally divided into two classes on the basis of their predominant function. Primary brighteners are materials used in very low or relatively low concentration, such as 0.002 to 2 g./l. and which by themselves may or may not produce any visible brightening action. Those primary brighteners which may exhibit some brightening efiects generally also produce deleterious side effects such as reduced cathode efficiency, poor deposit color, deposite brittleness and exfoliation, very narrow bright plate range, or failure to plate any nickel at all on the low current density areas. Secondary brighteners" are materials which are ordinarily used in appreciably higher concentrations than primary brighteners, such as 1 to 30 g./l. These materials, by themselves, may produce some brightening or grain refining effects, but the deposits are not usually mirror bright and the rate of brightening is usually inadequate.

Ideally, when primary and secondary brighteners of properly chosen and compatible nature are combined, fully bright, ductile deposits over a wide current density range are obtained which exhibit a good rate of brightening. This rate of brightening may vary from" low, medium to high, with the latter preferrediwhen maximum luster is desired with, a. of thickness of. nickel applied. Similarly, therate oflevelling' may'vary from low; medium to high, depending on the particular cooperating additives. chosen. The concentrations of the secondary brightenersmay. vary within fairly. wide limits, i.e., their concentrations are not. usually critical. The

2,986,500 Patented May 30, 1961 concentrations of the primary brighteners must usually be maintained within fairly narrow limits in order to maintain :such desirable deposit properties as good ductility, adequate low current density coverage, etc. Any bright nickel system which can be made less critical or more tolerant to fluctuations in primary brightener concentnations will have obvious advantages, particularly since the low concentration of primary brighteners and-the intrinsic chemical nature of some make strict control by chemical analysis difiicult. Any material of primary brightener nature or effectiveness which can'be used over fairly wide limits of concentrations is of great value in bright nickel plating.

Many fairly eflfective primary and secondary brightener combinations are known. However, most of them require excessively critical control for easy commercial use. I have now discovered a new brightener combination which possesses many advantages over those previously known.

It is an object of this invention to provide an efilci'ent process for electrodepositing bright and smooth nickel deposits.

Another object of this invention is to provide bath compositions for nickel plating from which bright nickel electrodeposits are obtained.

The invention also contemplates providing novel brightener combinations and compositions for use in nickel plating baths.

The invention contemplates electrodepositing' nickel from nickel containing baths to which have been added a small but effective amount of a primary brightener, a secondary brightener, and N-vinyl-2-pyrrolido'ne as an auxiliary secondary brightener.

N-vinyl-2-pyrrolidone is an unusual brightener. From baths containing it in combination with a secondary brightener, it is possible to obtain lustrous, but not mirror bright, deposits under limited conditions; particularly limited is the operative current density range. Haz'e is often encountered, usually in the lower current density range. Based on these limitations, it is impracticable to use such baths to" obtain acceptable bright deposits on the complex shapes generally encountered in commerce. It is possible to use such baths for obtaining s'emi biigh't deposits.

When N -vinyl-2-pyrrolidone is used in combination with small, effective amounts of primary brighteners, and With a secondary brightener, it augments, accentuates and improves their operational and brightening eliects; resulting in baths having outstanding bright nickel plating proper-ties. Mirror bright electrodeposits' may be produced from these baths over a wide range of conditions and concentrations. The critical factors which are objectionable and often limit the use of baths containing many conventional primary brighteners, in conjunction with the usual secondary brighteners, are largely obviated when N-vinyl-2 pyrrolidone is added to" the bath; Be tween: about 0.'O5'g./l. and 1.2 g./l. of N-vinyl-l-pyrrolidone in the bath is operative. The effect of the additive in the bath increases rapidly as its concentration is increased from about 0.05 g./l. to 0.2 g./l'. Increased concentrations, thereafter, only slowly increase the effectiveness of the additive. It is preferred to utilize baths containing between 0.2 g./l. and about 0.8 gL/l'. Toavoid'i-n suflicient concentration during operation'of the bath, it is preferable to attempt to maintain the concentration at about 0.5 g'./l. v

The primary brighteners 'usefulin conjunction with N- vinyl-Z-pyrrolidone' include, but are not limited; to such 3 materials as Z-mercapto-benzimidazole and substituted 2- mercapto-benzimidazole derivatives of the type disclosed in US. Patent 2,737,484. Another group are acetylenic alcohols of the type exemplified by 2-propyne-l-ol; 2- butyne-1,4-diol; 2 methyl-3-butyne-2-ol; 3-methyl lpentyne-3-ol; phenyl butynol; dimethyl octyne-diol; 3- phenyl-B-hydroxy-propyne-1; and compounds having the general formula R1C(CH3)(OH)CECC(OH) (CH )R wherein R may be hydrogen or a hydrocarbon radical having up to about 8 carbon atoms. The useful amount of these acetylenic compounds in the brightener composition varies with the compound specified. Thus, Z-propyne- 1-01 is used in amounts between 0.0025 g./l. and 0.01 g./l., and 2-butyne-1,4-diol is used in amounts between 0.005 g./l. and 0.01 g./l. It has been found that generally the 2-propyne-l-ol is a more effective agent than the 2-butyne- 1,4-diol, in that within the desired range, smaller quantities of the former are used to achieve the same degree of mirror brightness. Generally, the primary brighteners are used in amounts less than 0.02 g./l., and preferably not more than 0.015 g./l. Preferred primary brighteners are .2-rnercaptobenzimidazole, 5 amino 2 mercaptobenzimidazole, 6-mercaptopurine, 2 propyne-l-ol, 2-butyne-1,4- diol and alphaphenylpropynol.

As noted, N-vinyl-2-pyrrolidone has the unusual property of enhancing the effectiveness of the primary brighteners in the bath. Many materials have been tested as primary brighteners in the past and rejected although they exhibited fairly good brightening action, because the electro-deposit may not have attained quite the desired luster or brightness or the bath had some other defect. Many of these weak or not entirely adequate primary brighteners produce in combination with N-vinyl-Z-pyrrolidone, deposits and processes of outstanding quality. This becomes of great practical importance where these weak brighteners are cheap, easily available or synthesized, or have low rate of replenishment characteristics.

Secondary brighteners which can be used, generally in amounts between 1 g./l. up to 25 g./ 1., include substituted aromatic compounds such as 1,3,6-naphthalene trisulfonate, the sodium or potassium salts of ortho-sulfobenzaldehyde, orthosulfobenzyl alcohol, the water soluble aryl sulfonic acid and sulfonic acid compounds, etc. For use in high chloride type nickel plating baths, a preferred secondary brightener is the sodium or potassium salt of sulfonated dibenzothiophene dioxide.

Conventional baths and processes for electroplating bright nickel are described in Principles of Electroplating and Electroforming, Blum and Hogaboom, pages 362-381, revised third edition, 1949, McGraw-Hill Book Co., Inc., New York; and in Modern Electroplating,

edited by A. G. Gray, the Electrochemical Society, 1953, pages 299-355. The character, control and operating conditions, including the concentration of the bath ingredients, pH, temperature, cathode current density, etc., of these conventional baths are generally applicable to the present invention. Practically all baths for electroplating bright nickel contain nickel sul-fate, a chloride, usually nickel chloride; a buffering agent, usually boric acid; and a wetting agent, e.-g., sodium lauryl sulfate. Such baths include the well-known Watts type of bath and the high chloride type of bath. Other baths may contain as the source of the nickel a combination of nickel fluoborate with nickel sulfate and nickel chloride, or a combination of nickel fluoborate with nickel chloride. Typical range Watts-type baths and high chloride baths are noted in Tables I and II.

Table I Watts-type baths:

Nickel sulfate 200 to 400 g./l. Nickel chloride 30 to 75 g./l. Boric acid 30 to 50 g./l. Temperature 38 to C.

Agitation Mechanical, air, etc.

pH 2.5 to 4.5 electrometric.

4 Table 11 High chloride baths:

Nickel Chloride to 300 g./l. Nickel sulfate 40 to 150 g./l. Boric acid 30 to 50 g./l. Temperature 38 to 65 C. Agitation Mechanical, air, etc. pH 2.5 to 4.5 electrometric.

Best plating results are usually achieved in the electrodeposition process when a method is utilized of preventing thin film immediately adjacent to the cathode from becoming depleted in cation content. This is desirably accomplished by agitation, such as air agitation, solution pumping, moving cathode rod, etc.

For the purpose of giving those skilled in the art a better understanding of the invention, illustrative examples are given. In each of the examples, an aqueous acidic nickel containing bath was made up with specified components. Electrodeposition of nickel was carried out by passing a direct current through an electric circuit comprising an anode and a sheet metal or rod cathode, both immersed in the bath. The baths were agitated, usually by a moving cathode. Bright electrodeposits were obtained in all the tests included herein as examples.

In Examples 1 through 9, the following aqueous bath was used as a base solution:

The other bath components are given in tabular form in Table III. Standard processing conditions were utilized.

Table 111 Example Additives Amount, N0. g/l.

o-sulfobenzaldehyde (N a salt) 3 1 N-vinyl-2-pyrrolidone 0. 5 propargyl alcohol 0. 005 sodium lauryl sulfate 0. 25 o-sulfobenzaldehyde (Na salt) 3 2 N-vinyl-2pyrrolidone. 1. 0 propargyl alcohol 0. 005 sodium lauryl sulfate i i. 0. 25 sulfonated dibenzothiophene dioxide (Na salt).. 4 3 N-vinyl-Z-pyrrolidone 0. 5 2-mercapto benzimidazole 0. 01 sodium lauryl sulfate 0. 25 sulfonated dibenzothiophene 4 4 N-vinyl-Z-pyrrolidone 0. 2 2-mercapto benzimidazole- 0. 01 sodium lauryl sulfate O. 25 sulfonated dibenzothiophene dioxide (Na salt)" 4 5 N -vinyl-2-pyrrolidoue 1 5amino-2-mercaptc benzimiclazole 0.01 sodium lauryl sul 0. 25 sodium 1,3,6,naphthalene trisulfonate- 20 sulfonated dibenzothiophene dioxide (Na salt)" 1 6 N-viuyl-z-pyrrolidone 0. 2 2-mercapto benzimidazole 0. 01 sodium lauryl sulfate 0. 5 sodium l,3,6,naphthaleue trisulfunate 20 sulfonated dibenzothiophene dioxide (Na salt) 1 7 N-vinyl-2-pyrrolidoue 0. 2 (intercepts purine 0.007 sodium lauryl sulfate 0. 25 o-sulfobenzaldehyde (Na salt) 3 8 N-vinyl-Z-pyrrolidone 0. 2 6-mercapto purine 0.005 sodium lauryl sulfate 0.25 o-sulfobenzaldehyde (Na salt) 3 9 N-vinyl-2-pyrrolidone 0. 2 mphenyl propynol. 0.01 .sodium lauryl sulfate 0. 5

Examples 10 through 14 were carried out using standard conditions and the specified additives in a high chloride bath of the following composition:

Table IV Additives Amount,

suh'onated dlbenzothiophene dioxide (N a salt) N-viuyl-Z-pgrrolldone Z-mercapto enzimidazole sulfonated dibenzothiophene dioxide (Na salt) N-vinyl-2-pyn'olidone fi-amlno-Zmeroapto benzimldazole sulfonated dibenzothlophene dioxide a salt)-. N-vmyl-2-pyrro1idone 6-mercapto purine sulfonated dibenzothlo heue dioxide (Na salt) N-vinyl-2-pyrrolidone fi-mercapto purine {lulfonated dibenzothlophene dioxide (Na salt).-

N-vinyl-2-pyrrolidone a-phenyl-propynol ropargyl alcohol The foregoing examples illustrate specific baths and processes, several being preferred. It is understood that the compositions and conditions may be varied. Although the sodium salts were most often used and are preferred, they may be partially or completely replaced by such other salts as the potassium salts, etc.

The nickel electrodeposits obtained from baths utilizing the novel brightener combination are advantageous in that mirror-bright lustrous electrodeposits having a high degree of ductility are obtained over a wide range of current densities. The N-vinyl-Z-pyrrolidone, the new component of the combination, is relatively inexpensive and is readily available. It has the further advantage that the concentration in nickel plating baths is easily determined by a relatively simple analytical procedure. The bright nickel electrodeposits are preferably plated on a copper or copper alloy basis metal. However, they may be electrodeposited directly on such metals as iron, steel, etc.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

I claim:

1. In the process of electroplating nickel from nickelcontaining baths, the improvement which comprises incorporating in said baths between 1 g./l. and 25 g./l. of a secondary brightener characterized by having at least one group selected from sulfone and sulfonic acid groups attached to a nuclear carbon of a homocyclic aromatic ring, and between 0.05 g./l. and 1.2 g./l. of N-vinyl-Z- pyrrolidone, whereby lustrous nickel electrodeposits are obtained.

2. In the process of electroplating bright nickel from nickel-containing baths, the improvement which comprises incorporating in said bath between 1 g./l. and 25 g./l. of a secondary brightener characterized by having at least one group selected from sulfone and sulfonic acid groups attached to a nuclear carbon of a homocyclic aromatic ring, between 0.0025 g./l. and 0.02 g./l. of a primary brightener selected from the class consisting of 2-mercapto benzimidazoles and acetylenic alcohols, and between 0.05 g./l. and 1.2 g./l. of N-vinyl-2-pyrrolidone as an auxiliary secondary brightener, whereby bright nickel electrodeposits are obtained.

3. In a nickel-containing bath for nickel plating, the combination therewith of between 1 g./l and 25 g./l. of a secondary brightener characterized by having at least one group selected from sulfone and sulfonic acid groups attached to a nuclear carbon of a homocyclic aromatic ring, and between 0.05 g./l and 1.2 g./l. of N-vinyl-2- pyrrolidone as an auxiliary secondary brightener.

4. In a nickel-containing bath for bright nickel plating, the combination therewith of between 0.0025 g./l. and 0.02 g./l. of a primary brightener selected from the class consisting of a Z-mercapto benzimidazoles and acetylenic alcohols, between 1 g./l. and 25 g./l. of a secondary brightener characterized by having at least one group selected from sulfone and sulfonic acid groups attached to a nuclear carbon of a homocyclic aromatic ring, and between 0.05 g./l. and 1.2 g./l. of N-vinyl-2-pyrrolidone and as an auxiliary brightener.

5. The bath of claim 4 containing between 0.2 g./l. and 1.2 g./l. of N-vinyl-2-pyrrolidone.

6. The bath of claim 5 containing between 0.005 g./l. and 0.015 g./l. of a primary brightener.

7. The bath of claim 6 containing between 0.2 g./l. and .0.8 g./l. of N-vinyl-Z-pyrrolidone.

8. The bath of claim 7 utilizing an acetylenic alcohol as the primary brightener.

9. The bath of claim 7 utilizing Z-mercapto-benzimidazole as the primary brightener,

10. The process of claim 2 in which the primary brightener in the bath is present in an amount between 0.005 g./l. and 0.015 g./l.

References Cited in the file of this patent UNITED STATES PATENTS 2,712,522 Kardos et a1. July 5, 1955 2,737,484 Passal Mar. 6, 1956 2,852,449 Becking et al Sept. 16, 1958 

1. IN THE PROCESS OF ELECTROPLATING NICKEL FROM NICKELCONTAINING BATHS, THE IMPROVEMENT WHICH COMPRISES INCORPORATING IN SAID BATHS BETWEEN 1 G./L. AND 25 G./L. OF A SECONDARY BRIGHTENER CHARACTERIZED BY HAVING AT LEAST ONE GROUP SELECTED FROM SULFONE AND SULFONIC ACID GROUPS ATTACHED TO A NUCLEAR CARBON OF A HOMOCYCLIC AROMATIC RING, AND BETWEEN 0.05 G./L. AND 1.2 G./O. OF N-VINYL-2PYRROLIDONE, WHEREBY LUSTROUS NICKEL ELECTRODEPOSITS ARE OBTAINED. 